An apparatus of this type is known from U.S. Pat. No. 3,052,228. In the known apparatus, the water level can be adjusted manually using an adjusting device. On the outlet side, only a faucet is provided, which enables the emptying of the container under the influence of the gravitational force of the heated water located in it.
The known apparatus may be adequate for certain applications, such as in camping. It is inadequate, however, for meeting the need for large quantities of hot water to be supplied to household water systems, and so cannot provide a true alternative to conventional hot water systems.